In whisky production, there is very little information regarding the influence of wort
insoluble material on the fermentation. Therefore, an investigation into the influence of
wort solid material on the fermentation of whisky wort by yeast was undertaken. Initial
studies involved assessing the effects of wort solids on a small-scale fermentation system.
Fermentation parameters, such as decrease in wort specific gravity (SG) and free-amino
nitrogen (FAN) were assessed during fermentations of clarified and cloudy wort. Results
showed fermentation of cloudy wort to be faster and more complete. Shaking
fermentations of clear wort appeared to negate these effects, allowing fermentation to
proceed like that of cloudy wort, but differences in the amount of FAN consumed were
apparent. Clarification of wort by centrifugation resulted in altered fermentation
parameters compared to addition of wort solids back to clear wort, suggesting a role for
the physical nature of the solids. Clarified wort was shown to contain an elevated C02
concentration after 5 and 8 hours fermentation (ca. 5 g/L), but addition of an inert
material (diatomaceous earth (DE)) decreased the concentration to levels observed in
cloudy wort (ca. 2 gIL). Bentonite, another inert material, did not have the same ability as
DE. Environmental Scanning Electron Microscopy revealed that the solids with porous
surface topography (wort solids and DE) were more effective as CO2 nucleating agents.
Static 1L fermentations of whisky wort were also carried out. A model was devised
whereby clear wort was supplemented with DE at a concentration similar to that of solids
in cloudy wort. Differences during fermentation were still apparent between cloudy wort
and clear wort with DE, which could not be accounted for by elevated C02 concentrations. A series of fermentations were performed where clear wort with DE was
supplemented with long chain fatty acids and fermented in conjunction with cloudy wort.
There were no apparent effects after addition of hexadecanoic, octadecadienoic and
octadecatrienoic acids, but fermentation was enhanced with the addition of the
unsaturated fatty acids hexadecenoic acid and octadecenoic acids. Zinc addition enhanced
fermentation slightly, but not to the same level as cloudy wort.
The effects of differences in mashing technique in a commercial setting were
investigated. There was a decrease in the initial concentration of FAN in worts where the
first sparge temperature was 90°C, as opposed to 76 °C, and a higher concentration of
solids and long-chain fatty acids. These worts fermented more quickly, in terms of
consumption of FAN by yeast, during early fermentation. Differences were also observed
in the concentration of volatiles (esters and higher alcohols) between worts after 50 hours
fermentation. Dielectric measurements taken over a 72 hour, temperature-controlled
fermentation period revealed fundamental differences in yeast cell behaviour during
fermentation of wort from different distilleries. Worts were also produced in the 2 hL
pilot plant at Heriot-Watt University, Edinburgh, to determine the effects of experimental
differences in mashing regime on the subsequent wort. Again, fundamental differences
were observed during fermentations, which appeared to be linked to differences in the
components present in different worts. From these results it was hypothesised that the
ability of yeast to consume and utilise a range of compounds in wort would render them
more resistant to stress, particularly when more fatty acids were available.